When a Mortgage Servicer files a Notice of Election and Demand (NED) it is listed with the County Treasurer or Assessor (at least in Colorado). This is part of the process they have to go through to notify the Homeowner/Borrower that their home is starting the Foreclosure process and it must be listed publicly. It's just a check and balance that is in place so the bank can't really just show up and kick a homeowner out of their home (contrary to popular media coverage).
Typically the NED is filed after 3 missed payments, but I've heard of quite a few banks (Countrywide/BofA) that have let borrowers go several months without making payments before filing the NED.
Once the NED is filed, the clock starts for the Redemption or Cure period which allows the homeowner/borrower to either Pay & Stay, or Sell & Go. Those typically are the two options for a homeowner once they have hit the NED. Nowadays the third option is a Loan Modification and that often times will drag out the NED being filed.
I get a good list of NED filings from my Title Company and it's in an excel format with addresses, loan amounts, banks, etc. Very nice.
Hope that helps,